Crash diets 'work best' claim misguided

“Crash diets DO work, claim experts,” the Mail Online reports.

It reports on an Australian study involving 200 obese adults who were randomly assigned to either a 12-week rapid weight loss programme on a very low-calorie diet or a 36-week gradual weight loss programme.

It found that 81% of people in the rapid weight loss group achieved the target weight loss (more than 12.5% of their bodyweight), compared to 50% of those in the gradual weight loss group.

Participants, from both groups, who lost more than 12.5% of their bodyweight were then placed on a weight maintenance diet for three years. However, 71% of the weight was regained in both groups after this three-year period.

So it would appear, whatever the weight loss regime used, that the real challenge is keeping off the weight in the long term.

The study may also not have captured the harmful effects that may be associated with rapid weight loss, such as loss of muscle mass or poor nutrition.

If carefully supervised, very low-calorie meal replacements may be suitable for some people with obesity, at least as an initial measure, but they are not a long-term solution.

The NHS Choices weight loss plan uses a combination of not just diet, but also exercise and lifestyle changes, to achieve sustainable and prolonged weight loss.

Where did the story come from?

The study was carried out by researchers from the University of Melbourne and La Trobe University, Australia. It was funded by the Australian National Health and Medical Research Council and the Sir Edward Dunlop Medical Research Foundation.

One of the authors of the study has a history of previous employment with Nestle’s Optifast. Optifast was used as the low-calorie food substitute for the rapid weight loss group. Though Nestle played no role in either the funding, design or analysis of the study.

The study was published in the peer-reviewed medical journal The Lancet Diabetes and Endocrinology.

The study was covered widely and not always accurately in the media. The message in The Daily Telegraph that “crash diets” are more effective than gradual weight loss is misleading. Though more people achieved the target weight loss in the rapid weight loss group initially, in the long-term maintenance phase of the trial, 71% of both groups regained the weight they had lost.

Encouraging all people to go on crash diets is inadvisable – it should be pointed out that in this study, participants were carefully supervised by professionals experienced in treating obesity.

Reassuringly, most sources included information regarding the potential risks of low-calorie diets such as kidney damage and lack of adequate nutrition.

What kind of research was this?

This was a randomised controlled trial (RCT), which aimed to compare the effect of rapid and gradual weight loss programmes on both the rate of weight loss and the rate of weight regain in obese people.

The authors say that guidelines recommend gradual weight loss for the treatment of obesity on the grounds that weight lost rapidly is more quickly regained. However, there is evidence to suggest that this is not necessarily the case.

This RCT took place in two phases: an initial phase where people followed a rapid weight loss or gradual weight loss programme, followed by a second phase where those who had achieved the target weight loss entered the same longer-term maintenance phase.

What did the research involve?

The two phase trial took place between 2008 and 2013. It included 200 obese adults who were otherwise healthy and aged between 18 and 70 years. In the first phase, 103 participants were randomly assigned to a 12-week rapid weight loss (RWL) programme on a very low-calorie diet (450-800 kcal per day), and 97 were assigned to a 36-week gradual weight loss (GWL) programme, which reduced energy intake by 400 to 500 kcal a day, in line with current dietary guidelines in Australia, where the study took place.

Those in the RWL group consumed a commercially available "very low energy" meal (Optifast) instead of the usual three meals a day, following the manufacturer’s recommendations. The aim for this group was 15% weight loss during the 12 weeks (about 1.5kg per week). In the GWL programme, participants used one to two of the commercial meal replacements with the aim of 15% weight loss over 36 weeks (about 0.5kg per week).

All participants received the meal replacements free, and were given similar material on dietary education.

Those who achieved 12.5% weight loss or more in the allocated timeframe were eligible to enter the second phase of the trial, which continued for 144 weeks. In this phase, participants were instructed to follow an individualised diet for weight loss maintenance, based on Australian guidelines. They had individual sessions with dieticians at weeks four and 12 and then every 12 weeks. Adherence to the diet was assessed and those regaining lost weight were advised to follow an energy reduced diet (400-500 kcal a day less).

Throughout the study all participants were instructed to take 30 minutes or more daily of mild to moderate intensity exercise. Physical activity was measured using a pedometer worn for seven consecutive days.

Total study duration was three years for the RWL group and 3.5 years for the GWL group.

The main outcome examined was the average weight loss maintained at week 144 of the trial, in the second phase. Participants were weighed after fasting overnight. Their waist and hips were measured and their body composition analysed. Other outcomes examined were blood levels of certain hormones associated with appetite (ghrelin and leptin), and participants’ subjective appetite.

In their analyses, they looked at only those who had completed the trial, and carried out intention to treat analysis (ITT), in which all participants are included in the results, whether or not they have dropped out.

What were the basic results?

In the first phase of the trial, more participants in the rapid weight loss group achieved the target weight loss and started phase two of the trial (76 people; 81%) compared to participants in the gradual weight loss group (51; 50%)

However, at the end of the weight maintenance phase, there was no difference between groups in the proportion who regained weight. Looking at only those who completed the study (43/51 in GWL and 61/76 in RWL), roughly equivalent proportions in each group had regained most of their lost weight: 71.2% of the gradual weight loss group (95% confidence interval [CI] 58.1 to 84.3), and 70.5% of the rapid weight loss (95% CI 57.8 to 83.2).

Intention-to-treat analysis showed similar results: gradual weight loss 76.3% regain (95% CI 65.2 to 87.4) vs rapid weight loss 76.3% regain (95% CI 65.8 to 86.8).

Looking at adverse effects, during the first phase of the trial one person in the rapid weight loss group developed acute cholecystitis (gallbladder inflammation) and had to have their gallbladder removed. This adverse effect was considered to be “probably related to the rapid weight loss programme”.

During the second phase of the trial, two people in the rapid weight loss group developed cancer (multiple myeloma and breast cancer), but these adverse effects were not considered to be related to the dietary intervention.

How did the researchers interpret the results?

The researchers say their findings show that the rate at which weight is lost does not affect the rate at which it is regained during the weight loss maintenance period. These findings, they say, are not consistent with current dietary guidelines, which recommend gradual rather than rapid weight loss. They also point out that RWL was more likely to lead to target weight loss and fewer drop outs.

They say it is possible that low-energy meals are easier to follow because fewer choices have to be made than for a diet consisting of regular foods. The limited carbohydrate intake of very low-calorie diets may induce ketosis (where the body uses fat for energy), which might promote feelings of fullness. Losing weight quickly may also motivate people to persist with their diet and achieve better results, they argue.

The authors say that long-term weight regain is probably caused by a rise in levels of the hormone ghrelin after a weight loss programme. Experts should now focus on the safety of appetite suppressants to help prevent weight regain, they say.


This study challenges the widely held view that losing weight gradually, as recommended in current guidelines, results in better long-term weight reduction and less weight regain compared to losing weight rapidly using a very low-calorie diet.

The study found that though initially more people in the rapid weight loss group achieved the target weight loss compared to the gradual weight loss group, when these participants then entered the longer-term maintenance phase where all followed individualised diets. Equivalent proportions in each group then regained weight.

The sad fact seems to be that whatever type of diet is followed, maintaining weight loss in the long term is the real challenge.

The study had some limitations. As the authors point out, the main weakness was its exclusion of people who smoked, had diabetes, took weight-altering drugs or were severely obese. Many people with obesity also have diabetes and are often smokers. This makes it difficult to know if the results are generalisable to the average person seeking medical assistance with weight loss.

It is also important to recognise that this study may not have captured the harmful effects that may be associated with rapid weight loss. This study did observe that one person in the rapid weight loss group developed acute gallbladder inflammation, and this was attributed to the weight loss programme being followed. Rapid weight loss can also result in greater loss of muscle mass, and a very low-calorie diet may be short of essential nutrients.

It is possible that for some obese adults, a carefully supervised very low-calorie diet may be a suitable option, at least as an initial measure, but they are not a long-term solution and do not solve the goal of long-term maintenance of a healthy weight.

The best way to achieve a healthy weight and maintain it in the long term is likely to involve a long-term commitment to a lifestyle change, involving a healthy, balanced diet with regular exercise in line with government recommendations.

NHS Attribution